Embodiments of the present invention refer to a method for operating a programmable metallization cell. Embodiments of the present invention further relate to a memory circuit including a programmable metallization cell.
Memory cells including a solid electrolyte material are well known as PMC (programmable metallization cell) memory cells. Memory devices including such PMC memory cells are known as conductive bridging random access memory (CBRAM) devices. The storing of different states in a PMC memory cell is based on the developing or diminishing of a conductive path in the electrolyte material between electrodes based on an applied electrical field. Although the electrolyte material may typically have a high resistance, the conductive path between electrodes may be adjusted to have a low resistance. Thus, the PMC memory cell may be set to different states depending on the resistance of the PMC memory element. Typically, both states of the PMC memory cell are sufficiently time-stable in such a way that data may permanently be stored.
A PMC memory cell is typically operated by applying a positive or a negative voltage to the solid electrolyte of the PMC memory element. To store data into the PMC memory cell, the PMC memory cell is brought to a programmed state by applying a suitable programming voltage to the PMC memory cell which results in the creation of the conductive path in the electrolyte material and which may correspond to the setting of a first state with low resistance. In order to store a second state in the PMC memory cell with high resistance, an erase voltage may be supplied in such a manner that the resistance of the PMC memory cell changes back to a high resistance which may correspond to a second state with a high resistance (e.g., an erased state). To read out a PMC memory cell, a read voltage may be applied which may be lower than the programming voltage. With the read voltage, a current through the resistance of the PMC memory element may be detected and associated to the respective low or high resistance state of the PMC memory cell.
A programming circuit may be used to access the PMC memory cell. The circuit may be configured to provide a reversible bias across the microelectronic device to perform erase and write functions. One configuration of the programming circuit may include one or more inputs and a complementary metal-oxide semiconductor circuit coupled to the programmable device. This design may allow for writing and erasing of the programmable cell using a low and a high voltage input. To program a first state into the PMC cell, a high voltage may be applied to the anode and a low voltage may be applied to the cathode. To program a second state into the PMC cell, a low voltage may be applied to the anode and a high voltage may be applied to the cathode of the PMC cell.
What is needed are improved methods and apparatuses for programming a PMC memory cell.